US 7971351 B2
The objective of the invention is to provide a method of manufacturing a semiconductor device that allows individual molding of plural semiconductor chips carried on a surface of the substrate. It includes the following process steps: a process step in which plural semiconductor elements 102 are arranged on the surface of substrate 100; a process step in which the inner side of substrate 102 is fixed on lower die 130; a process step in which liquid resin 114 is supplied from nozzle 112 onto each of the semiconductor elements in order to cover at least a portion of each of semiconductor chips 102; a process step in which the upper die having plural cavities 144 formed in one surface is pressed onto the lower die, and liquid resin 114 is molded at a prescribed temperature by means of plural cavities 144; and a process step in which cavities 144 of upper die 140 are detached from the substrate, and plural molding resin portions are formed individually.
1. A method of manufacturing a semiconductor device; comprising:
disposing a plurality of semiconductor elements on a first surface of a substrate;
placing the substrate on a lower die;
dispensing liquid resin on the substrate to form a plurality of domes each covering one semiconductor element; each dome containing a quantity of liquid resin for one semiconductor device;
lowering an upper die to press onto the substrate and confining each individual dome of liquid resin in a recess; in which the liquid resin has a glass transition temperature in the range of 100-160° C., a coefficient of thermal expansion in the temperature region below the glass transition temperature in the range of 20-30 ppm, a coefficient of thermal expansion in the temperature region above the glass transition temperature in the range of 80-120 ppm, a longitudinal modulus in the temperature region below the glass transition temperature in the range of 1-20 GPa, and a longitudinal modulus in the temperature region above the glass transition temperature in the range of 0.1-1.0 GPa;
lowering a pressing member on the liquid resin; and
curing the liquid resin to form semiconductor devices having flat tops.
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This application is a continuation of application Ser. No. 11/426,622, filed Jun. 27, 2006, now Issued as U.S. Pat. No. 7,520,052, the contents of which are herein incorporated by reference in its entirety.
The present invention is concerned with the methods for sealing plural semiconductor chips mounted on one surface of a substrate, especially a molding method which can be adapted for the development of small, thin semiconductor devices.
The popularity of cell phones, portable computers, and other small electronic equipment, has created ever-increasing demand for the development of small, thin semiconductor devices installed in them. In order to meet this demand, researchers have developed BGA and CSP packages, which have been adopted in practical applications.
Patent Reference 1 discloses a type of BGA package. As shown in
Also, Patent Reference 2 discloses a type of molding die that performs resin molding for workpieces to be molded having plural semiconductor chips mounted in a matrix shape on one surface of the substrate, and a resin molding method using said molding die.
However, the aforementioned molding methods of the prior art have the following problems. As shown in
Also, the stacked IC package assembly form has become popular. A stacked IC package is supplied through a reflowing oven while it is assembled on a mother substrate, exposing it to a high temperature. As a result, the difference in thermal expansion coefficients of the principal materials used in the package cause mechanical warping. This warping prevents the terminals of the package (solder balls) from making contact with the terminals on the mother substrate, leading to contact defects.
Stacked IC packages usually make use of the transfer molding scheme. In this scheme, hot liquefied resin is poured into an injection port known as a gate, and the gate is mechanically cut after partial curing of the resin in order to form an integral molding. Because the gate is cut mechanically, the outer dimensional accuracy and the appearance of the package may become defective. In addition, residual resin is created after resin sealing, and this leads to poor assembly when the IC package is stacked.
The objective of the present invention is to solve the aforementioned problems of the prior art by providing a method of manufacturing a semiconductor device that allows individual molding of plural semiconductor chips mounted on one surface of a substrate.
In addition, the objective of the present invention is to provide a method of manufacturing a semiconductor device that can make the molded resin over the plural semiconductor chips mounted on one surface of the substrate be small and thin.
In addition, the objective of the present invention is to provide a type of semiconductor device and its manufacturing method that allows another surface assembly type of semiconductor device to be stacked on the surface where the molding resin is formed.
The present invention provides a method of manufacturing a semiconductor device characterized by the following facts: in a method of manufacturing a semiconductor device wherein semiconductor elements are mounted on a substrate sealed with a resin, plural semiconductor elements are arranged on the first principal surface of the substrate; the second principal surface opposite to the first principal surface of the substrate is fixed on a supporting part (lower die); a liquid resin is supplied to each of the semiconductor elements to cover at least a portion of each semiconductor element; a mold part (upper die) having plural recesses (cavities) formed in one surface is pressed onto the supporting member, and the liquid resin for each semiconductor element is molded within each said recess at a prescribed temperature; and the recesses of the mold part are released from the substrate.
The process step in which the liquid resin is supplied includes a process step in which a nozzle for supplying liquid resin is driven to scan the first principal surface of the substrate. It is preferred that the quantity supplied be in the range of ±3% with respect to the volume of the recess of the mold part. Also, it is preferred that the liquid resin be in liquid form at room temperature, and it have a viscosity in the range of 30-150 Pa□s.
The liquid resin is molded at about 150° C. In this case, a flexible film may be adhered on the plural recesses of the mold part. The flexible film acts as a mold release material for the molding resin. It is preferred that the softening temperature of the film be near the temperature at which the liquid resin is molded. In addition, the surface of the film that is to contact the plural recesses is rough, and the film is preferably at least 50 μm thick so that it can cover the steps formed on the substrate. For example, the film is made of a thermoplastic fluorine-containing resin (ETFE).
For the manufacturing method, it is preferred that there also be a process step in which the atmosphere around the liquid resin is evacuated before molding the liquid resin by means of the recesses of the mold part. Because the atmosphere of the semiconductor element is evacuated, it is possible to inhibit gas bubbles and voids in the molding resin. The degree of absolute vacuum is 5 kPa or better.
In addition, the mold part contains plural pressing members with recesses formed in them, and the various pressing members are independently supported in an elastic way. The liquid resin supplied to each semiconductor element is pressed individually.
The manufacturing method also includes a process step in which the substrate is cut to correspond to the area of the molded semiconductor elements, a process step in which connecting terminals are attached on the second principal surface, and a process step in which another semiconductor device is stacked onto the first principal surface of the substrate.
The semiconductor device of the present invention has another semiconductor device stacked onto the semiconductor device manufactured in the aforementioned process step. In this case, a wiring pattern is formed on the first principal surface of the substrate, and the plural connecting terminals formed on the inner surface of another semiconductor device are electrically connected to the aforementioned wiring pattern. For example, the connecting terminals of said another semiconductor device are for BGA or CSP packages, and these terminals are arranged on the outer periphery of the molding resin. As a result, the molding resin is sandwiched between the substrate of said semiconductor device and said another semiconductor device.
In the figures, 100 represents a substrate, 102, 210, 304, 306 represent semiconductor chips, 104, 212 represent bonding wires, 110 represents a container, 112 represents a nozzle, 114 represents a liquid resin, 130 represents a lower die, 140 represents an upper die, 142 represents a release film, 144 represents a cavity, 146 represents a pressure member, 150 represents an air suction hole, 152 represents a leg portion, 160, 184, 206, 410 represent molding resin, 170, 186 represent chamfers, 180 represents an air pocket, 182 represents a land, 188 represents a protrusion, 200 represents a first semiconductor device, 202 represents a multilayer wiring substrate, 204 represent solder balls, 208 represents a die attachment, 300 represents a second semiconductor device.
According to the present invention, it is preferred that resin sealing of the plural semiconductor elements formed as a block on one surface of the substrate be performed individually. As a result, it is possible to provide a small, thin semiconductor device. In addition, because plural semiconductor elements are individually sealed by resin, it is possible to prevent waste of the molding resin. At the same time, it is possible to obtain individual semiconductor devices without dicing the molding resin, so that the shear stress or the like that results when the molding resin is cut is not directly applied. Consequently, no cracks are generated in the molding resin, the dimensional accuracy of the molding resin becomes consistent, and a high-quality appearance can be guaranteed.
In the following, preferred embodiments of the present invention will be explained with reference to figures.
In the following, the method will be explained for individually molding said semiconductor chips 102 mounted on the substrate shown in
With regard to the characteristics of liquid resin 114, it is in liquid form at room temperature, and its viscosity is about 30-150 Pa□s, or preferably 45 Pa□s. A consistent viscosity for liquid resin 114 makes it possible to effectively cover the entirety of semiconductor chip 102 with liquid resin 114 supplied from the nozzle. For example, one may make use of an epoxy resin as liquid resin 114, and it can have quick-curing properties.
Then, as shown in
Release film 142 is then prepared on the pressure surface side of upper die 140. Plural recesses, that is, cavities 144, are formed in the pressure surface side of upper die 140. These cavities 144 are arranged corresponding to the positions of semiconductor chips 102 on the substrate fixed on the lower die. Pressing member 146 is provided in each cavity 144, and pressing member 146 is elastically supported by spring 148. Said cavity 144 is a rectangular recess surrounded by the pressure surface of pressing member 146 and the side surfaces of leg portions 152, and it defines the outer shape of the molded molding resin. For example, the dimensions of cavity 144 surrounded by the side surfaces of leg portions 152 and by pressing member 146 are 10.9 mm in width, 10.9 mm in length, and 0.27 mm in height. Also, for example, the dimensions of semiconductor chip 102 are 8.8 mm in width, 8.6 mm in length, and 0.1 mm in height.
In addition, air suction hole 150 connected to each cavity 144 is formed in upper die 140. By sucking air through said air suction hole 150, release film 142 is sucked in and adhered along the pressure surface of cavity 144 of upper die 140.
Said release film 142 is supplied from reel 154, and it is taken up by reel 156 (see
Also, it is preferred that release film 142 be at least 50 μm thick. As will be explained later, when liquid resin 114 is molded, release film 142 is pressed against substrate 100 by leg portion 152. In this case, liquid resin 114 does not squeeze out from the contact interface between release film 142 and substrate 100. A copper pattern and solder resist are formed on the surface of substrate 100, creating a step of about 20 μm from the surface of the substrate. The thickness of release film 142 is selected to be 50 μm or greater or sufficient to cover the step. More specifically, one surface of release film 142 is processed to roughen it. For example, the roughness can be Rz: 15 μm. The surface that has been processed to roughen it is in contact with upper die 140. As a result, after molding of the liquid resin, release film 142 can be released easily from upper die 140 and wound up on reel 156.
Then, as shown in
Then, as shown in
Then, as shown in
Then, as shown in
The subsequent process steps include a process step in which solder balls are connected to the inner surface of substrate 100 as connecting terminals, and a process step in which the substrate is diced. In the dicing process step, the substrate is cut along dicing lines C positioned between molding resin portions 160, 160. That is, molding resin 160 is not cut in the dicing process step. Consequently, the outer shape of molding resin 160 can keep the shape of the cavity as is. As a result, it is possible to eliminate the generation of particles, cracks in the molding resin, and other problems.
In the following, a second embodiment will be explained. In the first embodiment, the internal shape of cavity 144 (recess) of upper die 140 is rectangular. In Embodiment 2, air pockets are formed at the chamfers at the corners of each cavity 144.
In this embodiment, it is possible to eliminate the generation of voids in molding resin 184 by providing air pockets 180. Consequently, it is possible to increase the package yield. The size of air pocket 180 should be appropriate to provide a prescribed volume for absorbing the voids. The acceptable size should permit said fine protrusion 188 to be separated by a prescribed distance D from land 182.
In the following, a third embodiment of the present invention will be explained.
Said first semiconductor device 200 has a BGA package composed of multilayer wiring substrate 202 0.3 mm thick, plural solder balls 204 0.23 mm high formed on the inner surface of multilayer wiring substrate 202, and molding resin 206 formed on the upper surface of multilayer wiring substrate 202. On the upper surface of multilayer wiring substrate 202, semiconductor chips 210 are attached via die attachment 208, and the electrodes of semiconductor chips 210 are connected to copper pattern 214 on the substrate by means of bonding wires 212. The region containing semiconductor chip 210 and bonding wires 212 is sealed with molding resin 206. The loop height of bonding wires 212 from the chip surface is about 0.05 mm. The distance from bonding wires 212 to the surface of molding resin 206 is about 0.095 mm, and the height of the entire package of the first semiconductor device is 0.8 mm.
Second semiconductor device 300 is stacked on said first semiconductor device 200. For example, said second semiconductor device 300 has semiconductor chips 304, 306 stacked on the upper surface of substrate 302 and has said semiconductor chips 304, 306 sealed by molding resin 308. Said molding resin 308 may be of the transfer molding type. Two rows of solder balls 310 are formed in 4 directions on the inner surface of substrate 302.
When second semiconductor device 300 is stacked on first semiconductor device 200, solder balls 310 are arranged surrounding molding resin 206. Solder balls 310 of the second semiconductor device are connected to electrodes 216 formed on the upper surface of substrate 202 of first semiconductor device 200. The height of molding resin 206 from the surface of substrate 202 is about 270 μm, and the height of solder balls 310 from substrate 302 is a little larger. As a result, a small gap is formed between the inner surface of substrate 302 and molding resin 206.
In this way, when the manufacturing method of Embodiment 1 is adopted, by stacking the second semiconductor device on first semiconductor device 200 with very thin and small molding resin 206, it is possible to obtain a thin POP structure. It is similarly possible to obtain a thin POP structure using the manufacturing method of Embodiment 2.
In the following, a fourth of the present invention will be explained. When semiconductor device 200 manufactured using the method in Embodiment 1 (see
In this embodiment, in order to reduce warping h1, h2 of the substrate, a liquid resin is selected with the characteristics shown in
In this constitution, the magnitudes of semiconductor device warping at room temperature (for example, 25° C.) h1 and h2 are 80 μm or less, and the warping magnitudes h1, h2 of the semiconductor device at high temperature (for example, 260° C.) are 110 μm or less. As a result, good solder contact can be realized during substrate assembly.
Preferred embodiments of the present invention have been explained in detail above. However, the present invention is not limited to these embodiments. Various modifications and changes can be made as long as they remain within the scope of the present invention described in the claims.
In the aforementioned embodiments, the method of manufacturing BGA or CSP type semiconductor devices has been described. However, other types of semiconductor devices may also be adopted. There is no special limitation on the constitution of the package, and it is only required that the semiconductor chips carried on one surface of the substrate be sealed by resin. In addition, with regard to the method of assembling the semiconductor chips on the substrate, in addition to the connection method using wire bonding, connection can also be performed by means of the face-down scheme. In addition, in the aforementioned embodiments the cavities formed in the upper die are rectangular. However, the cavity may also have a sloping side surface so that the side surface of the resin molding is inclined.
The molding method of the semiconductor chip pertaining to the present invention can be used to substitute for the conventional transfer molding method and bonding method. By using the molding method of the present invention, an ultra-small and ultra-thin semiconductor device with high dimensional accuracy can be provided. In particular, it is possible to realize an ultra-thin semiconductor device of the surface assembly type.